* Size: The 351W is larger than the standard 289 or 200 cubic inch six-cylinder that came in '68 Mustangs. This means you might need to modify or replace the engine mounts and possibly the K-member (the front crossmember supporting the engine).
* Exhaust: The exhaust manifolds or headers will need to be specifically designed for a 351W in a '68 Mustang. Stock manifolds from other models likely won't fit.
* Steering: Depending on the accessories and headers used, clearance around the steering components might be an issue.
* Power Steering: You might need to adjust or replace the power steering pump and hoses.
* Transmission: The transmission needs to be compatible with the 351W. While a variety of transmissions could be used, you will have to account for their size and mounting needs.
In short, while physically possible, installing a 351 Windsor in a '68 Mustang is more involved than just dropping in an engine. It's a common swap, but requires planning and potentially professional help or significant mechanical experience. Researching specific parts and kits designed for this swap is highly recommended.
